Optical sensitization of photographic materials suitable for the silver-dyebleachingprocess



United States Patent ()fi ice 3,157,567 OPTICAL SENSZTEZATIGN 0F PHGTGGRAPEHC MATERIAL SUKTABLE F03 SlLVERBYE BLEACHHQG PRGCESS Heinrich Bruengger, Basel, and Helm t h oehl, li-ottrningen, Switzerland, assignors to Ciba Limited, Basel, Switzerland, 2 Swiss No Drawing. Filed Nov. 30, $59, der. N 356,617 Claims priority, application Switzerland, Dec. 4, 1958, 66,913 1 Claim. (Cl. %99) This invention provides a process for the optical sensitization of light-sensitive photographic layers that contain an aZo-dyestuil and are suitable for the silver-dye bleaching process.

It is known that single color or multi-color photo graphic (pictures) images can be produced by the silverdye bleaching process which depends on the destruction of dyestufi in accordance with the characteristics of the image. In that process an image is first recorded as a silver image by exposure and development by a normal photographic method in a light-sensitive layer uniformly colored with a dyestulf, and then the dyestutf present in the layer is locally destroyed by means of a silver-dye bleaching bath in proportion to the quantity of silver present locally. The silver is then removed to leave a dyestuff image that is the reverse of the original silver image. As in the case of color development processes that use multi-layer photographic materials, so also in the silver-dye bleaching process it is known to be of advantage to use for producing multi-color photographs a multi-layer material generally having three separate partial component color layers, of which the sensitivity is limited to different regions of the spectrum. A suitable multi-layer material contains, for example, on the support the red-sensitized layer containing the cyan dyestuff, upon that layer a green-sensitized layer containing a magenta dyestufi upon the latter layer a yellow filter layer to eliminate the action of the natural sensitivity of the layers beneath the filter layer, and as the uppermost layer a non-sensitized layer containing a yellow dyestulf.

In the silver-dye bleaching process an increase in the sensitivities of the several layers is especially important, because the light-sensitive silver halide layers each contain a dyestuff at the time of exposure, which dyestuff reduces the effective sensitivity of the layer by absorbing the exposure light. Such dyestutf-containing layers are very difiicult to sensitize owning to the fact that the dyestuffs in the layers have a strong desensitizing action on the emulsion in addition to the aforesaid reduction in sensitivity due to absorption.

In the process of this invention photographic layers suitable for use in the silver-dye bleaching process and having unexpectedly lzu'gh sensitivities are produced by incorporating as a sensitizer in a silver salt emulsion containing an azo-dyestuft a styryl or advantageously a cyanine dyestuff having a betaine-like structure. In such betaine-like dyestuffs the anion is present in the dyestufi molecule, and is thus bound by homopolar union to the Nall'.yl radical of the dyestuff. They are therefore zwitter ions or internal salts. As such cyanine dyestuffs of betaine-like structure there are advantageously used carboxy-betaine-cyanines, sulfo-betaine-cyarunes, or sulfatebetaine-cyanines, which may contain acid groups in addition to the aforesaid anion. There may also be used the corresponding styryl dyestuiis, i.e. carboxy-betainestyryl, sulfo-betaine-styryl or sulfate-betaine-styryl dyestutls.

Betaine-like dyestuffs of the above kind are known, see, for example, the disclosure of K. Mayer in Zeitschrift fiir wissenschaftliche Photographie, vol. 52 (1958), part 7-9, pages 176479. They have been used as sensitizers in gelatine emulsions containing color couplers. These emulsions were used for the production of photographic color images by color development. In such emulsions these betaine-like sensitizers are distin guished by the fact that their sensitizing action is not or is inappreciably changed by the presence of the color coupler. Nevertheless, it could not have been foreseen that such betaine-like sensitizers could be successfully used in emulsion layers containing azo-dyestulfs and suitable for the silver-dye bleaching process. Thus, it is known that azo-dyestuffs are generally more substantive in dyeing than are the colorless components used as couplers. This is especially true of polyazo-dyestulis (to which belong substantially all cyan azo-dyestulfs), which, owing to their hi h substantivity, have a strong tendency to displace sensitizers in the silver halide surface and so reduce the sensitivity. It would, therefore, be expected that, in the case of layers containing azodyestuffs, the adsorption of sensitizer on to the silver halide, which adsorption is essential for the sensitizing action, would be impaired or prevented by the strong tendency of the azo-dyestuff to be taken up substantively. Accordingly, it might have been considered that the azodyestuli would displace the sensitizer adsorbed on the silver halide or that the dyestufi would form an inactive compound with the sensitizer. It could certainly not have been expected that the use of betaine-like sensitizers in accordance with this invention would result in the very great improvement in sensitivity which is in fact obtained.

It was also known that azo-dyestufis possess an oxidizmg action and are therefore essentially desensitizers, and that they reduce the sensitivity attainable with ordinary cyanine dyestuffs.

The high sensitivities attainable in accordance with the invention are also attained in layers containing azodyestufis which are fixed by precipitation with basic recipitants, for example, biguanides. This is unexpected, because it is known that these basic precipitants (biguanide) possess a desensitizing action, and that therefore their presence in the emulsion would have been regarded as unfavorable to sensitization.

Essentially good results are also obtained with the use of azo-dyestufis which contain phenol groups. It has been known for a long time that azo-dyestutfs containing phenol groups have a harmful effect on the action of known sensitizers, probably on accout of the property of hydroxy-azo-dyestulfs existing in tautomeric form as hydrazones.

The method of sensitization in accordance with this invention is independent of the nature of the silver halide usedc Furthermore, there may be used as layer formers, in addition to the usual gelatine, other layer-forming colloids. The invention is not limited to the production of multi-layer material, and also applies to making emul- Patented Nov. 12?, i964 a d sionsconsisting of mixed granules. The emulsions may also contain so-called casting additions of various kinds,

for example, spreading agents, hardening agents or stabilizers.

The following examples illustrate the invention:

Example 1 100 grams of a silver bromide emulsion were sensitized for the long wavelength region of the spectrum with 1.0 milligram of a dyestufl having a betaine-like structure and of the formula (obtained according to the method described in German specification No. 1,028,718, filed by V. E. B. Filmfabrik bromide emulsion were sensitized for the long Wavelength region of the spectrum with 1.0 milligram of a dyestufi not having a betaine-like structure and of the formula to blue light (Wratten Filter No. 49) and to red light (Wratten Filter No. 29) developed and fixed.

Sensitometric examination showed that the light sensitive material sensitized in accordance with the invention had a considerably higher sensitization than the corresponding control material.

Relative sensitization (logarithmic values) With blue With red light light Example 1 2. 7 Control 2. 1

Example 2 200 grams of a 'silver bromide emulsion were sensitized for the region of the spectrum ranging from 500- 700 me with 3 mgs. of a dyestuff having a betaine-like structure and of the formula CH fHg CH2 $133 0 O- C O OH prepared according to Example 10 of German specification No. 892,965 to Agfa Leverkusen, Germany, granted September 3, 1953, and the emulsion was mixed with grams of a gelatine solution, which contained 6 grams of gelatine and 0.8 gram of a purple azo-dyestutf according to Schultz, Farbstolftabellen, 7th edition, vol. 11, page 48, E.I. 79 (C.I., Acid Red 131), and the emulsion was cast on a support. a

For the purpose of comparison 200 grams of a silver bromide emulsion were sensitized for the spectral region ranging from 500-700 my. with 3.0 mgs., of a dyestuff having a non-betaine-like structure and of the formula V (obtained as described by F. M. Hamer, Soc., 1927, page 2802), and the emulsion is mixed with 100 grams of a gelatine solution containing 6 grams of gelatine and 0.8 gram of the aforesaid purple azo-dyestuif (Colour Index, Acid Red 131), and the emulsion is cast on a support. The light-sensitive layer so produced serves 'for comparision with the emulsion prepared as described in the first paragraph of this example. Each emulsion was exposed to blue light (Wratten Filter No. 49) and green light (Wratten Filters Nos. 16 and 61) through a stepped wedge, and then developed and fixed.

Sensitometic examination showed that the light-sensitive material prepared as described in the first paragraph of this example had a considerably higher sensitization than the control material. 1

What is claimed is:

Photographic material having at least one light-sensitive silver halide emulsion layer containing an azo dyestufi containing phenolic hydroxyl groups and which is capable of being bleached out in the silver dye bleaching process and containing dyestufi selected from the group consisting of compounds of the formula V References Cited by the Examiner d an UNITED STATES PATENTS S S 2,054,390 9/36 Rust et a1 96-89 5 2,281,149 4/42 Gaspar 96-73 C CH=CH CH=C 2,503,776 4/50 Sprague 96106 2,612,496 9/52 Gasper 260-153 fi N 2,704,710 3/55 Sprung 96--73 E (13H: 2,912,329 11/59 Jones et a1. 96-106 H2 H2 10 NORMAN G. TORCHIN, Primary Examiner. g (500E HAROLD N. BURSTEIN, PHILIP E. MANGAN,

Examiners. 

